High power generators, especially of modern wind turbines, produce large amounts of thermal energy, which must be dissipated to avoid damage to, for example, the electrical insulation of the generator. The cooling systems of wind turbine generators are typically based on air cooling or closed circuit water cooling.
In US 2007/0024132 A1 a wind turbine generator comprising a stator with heat pipes integrated in the stator yoke is described. The heat pipes run in axial direction. The heat is absorbed or transferred from the components into an evaporator section of the heat pipe, particularly a vaporisable liquid in the heat pipe. The heat pipe is arranged with respect to a stator core such that the evaporator section extends into and is received within a bore which is configured to receive a corresponding heat pipe.
A system of axially oriented cooling slits for air cooling in the stator of a wind turbine is presented in EP 1 586 769 A2.
In EP 0 627 804 A2 a dynamoelectric machine comprising a plurality of stacked laminations without end plates forming a stator core with air ducts passing through the entire length of the stator is disclosed. The stacked laminations have a central bore for passage of a rotor there through and a plurality of winding slots extending radially outward from the bore. A plurality of cooling air passages extend axially through the stacked laminations generally parallel to the central bore. Each of the air passages are positioned adjacent to the terminating end of a corresponding one of the winding slots.
In U.S. Pat. No. 4,691,131 a stator of an AC motor with axially oriented passages for cooling liquid is described. The laminated core is impregnated with a resin to fill gaps between adjacent laminations and coat inner surfaces of the cooling liquid passages so that cooling liquid will flow through the cooling liquid passages without leakage therefrom.